The invention concerns a rheometer comprising a container for receiving a material sample to be investigated, and a rotary driven rotor which can be at least partially immersed into the material sample, wherein at least sections of an inner wall of the container have a profile.
In order to determine the rheological values of a material sample, the shearing stress and the deformation of the material sample must be exactly measured under a predetermined load and exactly defined ambient conditions. This is effected e.g. in a rotary rheometer as disclosed in U.S. Pat. No. 6,997,045 B2. A rotary rheometer of this type has a cup-like container into which the material sample is disposed. A rotary driven measuring shaft has a rotor at its lower end, which is immersed into the material sample. Rotation of the rotor within the material sample produces reaction forces and moments which are detected and from which the rheological characteristic material values of the material sample can be calculated, thereby taking into consideration the parameters of the surroundings.
In particular, in polydisperse suspensions, such as e.g. fresh building material suspensions, the metrological determination of the rheological properties is problematic, in particular, due to local demixing and associated sliding phenomena. These demixing phenomena can cause a very distinct localized change in the composition and thereby in the rheological properties of the material sample, and substantially falsify the measurement result. The extent of this problem depends on the composition of the examined material sample and also on the shearing stress which is produced in the contact zone between the material sample and the corresponding components of the rheometer.
In order to prevent formation of an undesired sliding zone, in particular, on the inner wall of the container, the inner wall of the container is conventionally provided with a profile. In particular, the inner wall surface of cylindrical sample containers, which are particularly suited for cement-containing suspensions, is provided with a groove structure having a depth of approximately 1 mm. This produces a toothing between the material sample and the inner wall of the container, which at least reduces the risk of sliding layer formation. In order to reliably prevent formation of a sliding layer, the profile of the inner wall of the container must be adjusted to the material being investigated. Since the groove structure is an integral component of the container, the profile cannot be adjusted to the material to be investigated.
It is the underlying purpose of the invention to provide a rheometer of the above-mentioned type with which the profile can be adjusted in a simple and fast manner to the type and properties of the material sample to be investigated.